Vinculin is required for cell polarization, migration, and extracellular matrix remodeling in 3D collagen

Comparison of vinculin tension in cellular monolayers and three-dimensional multicellular aggregates

Confocal frequency-domain fluorescence lifetime and Förster resonance energy transfer (FRET) microscopy of Chinese hamster ovary (CHO-K1) cells expressing the vinculin tension sensor (VinTS) is used to compare vinculin tension in three-dimensional (3D) multicellular aggregates and 2D cellular monolayers. In both 2D and 3D cultures, the FRET efficiency of VinTS is 5-6% lower than that of VinTL (p < 0.05), a tail-less control which cannot bind actin or paxillin. The difference between VinTS and VinTL FRET efficiency can be mitigated by treatment with the Rho-associated kinase inhibitor Y-27632, demonstrating that VinTS is under tension in both 2D and 3D cultures. However, there is an overall decrease in FRET efficiency of both VinTS and VinTL in the 3D multicellular aggregates compared with the 2D monolayers. Expression of VinTS in 2D and 3D cultures exhibits puncta consistent with cellular adhesions. While paxillin is present at the sites of VinTS expression in the 2D monolayers, it is generally absent from VinTS puncta in the 3D aggregates. The results suggest that VinTS experiences a modified environment in 3D aggregates compared with 2D monolayers and provide a basis for further investigation of molecular tension sensors in 3D tissue models.

B cell-based therapy produces antibodies that inhibit glioblastoma growth

Glioblastoma (GBM) is a highly aggressive and malignant brain tumor with limited therapeutic options and a poor prognosis. Despite current treatments, the invasive nature of GBM often leads to recurrence. A promising alternative strategy is to harness the potential of the immune system against tumor cells. Our previous data showed that the BVax (B cell-based vaccine) can induce therapeutic responses in preclinical models of GBM. In this study, we aimed to characterize the antigenic reactivity of BVax-derived Abs and evaluate their therapeutic potential. We performed immunoproteomics and functional assays in murine models and samples from patients with GBM. Our investigations revealed that BVax distributed throughout the GBM tumor microenvironment and then differentiated into Ab-producing plasmablasts. Proteomics analyses indicated that the Abs produced by BVax had unique reactivity, predominantly targeting factors associated with cell motility and the extracellular matrix. Crucially, these Abs inhibited critical processes such as GBM cell migration and invasion. These findings provide valuable insights into the therapeutic potential of BVax-derived Abs for patients with GBM, pointing toward a novel direction for GBM immunotherapy.

Micromechanics of fibrous scaffolds and their stiffness sensing by cells

Mechanical properties of the tissue engineering scaffolds are known to play a crucial role in cell response. Therefore, an understanding of the cell-scaffold interactions is of high importance. Here, we have utilized discrete fiber network model to quantitatively study the micromechanics of fibrous scaffolds with different fiber arrangements and cross-linking densities. We observe that localized forces on the scaffold result in its anisotropic deformation even for isotropic fiber arrangements. We also see an exponential decay of the displacement field with distance from the location of applied force. This nature of the decay allows us to estimate the characteristic length for force transmission in fibrous scaffolds. Furthermore, we also looked at the stiffness sensing of fibrous scaffolds by individual cells and its dependence on the cellular sensing mechanism. For this, we considered two conditions- stress-controlled, and strain-controlled application of forces by a cell. With fixed strain, we find that the stiffness sensed by a cell is proportional to the scaffold's 'macroscopic' elastic modulus. However, under fixed stress application by the cell, the stiffness sensed by the cell also depends on the cell's own stiffness. In fact, the stiffness values for the same scaffold sensed by the stiff and soft cells can differ from each other by an order of magnitude. The insights from this work will help in designing tissue engineering scaffolds for applications where mechanical stimuli are a critical factor.

Leader cells mechanically respond to aligned collagen architecture to direct collective migration

Leader cells direct collective migration through sensing cues in their microenvironment to determine migration direction. The mechanism by which leader cells sense the mechanical cue of organized matrix architecture culminating in a mechanical response is not well defined. In this study, we investigated the effect of organized collagen matrix fibers on leader cell mechanics and demonstrate that leader cells protrude along aligned fibers resulting in an elongated phenotype of the entire cluster. Further, leader cells show increased mechanical interactions with their nearby matrix compared to follower cells, as evidenced by increased traction forces, increased and larger focal adhesions, and increased expression of integrin-α2. Together our results demonstrate changes in mechanical matrix cues drives changes in leader cell mechanoresponse that is required for directional collective migration. Our findings provide new insights into two fundamental components of carcinogenesis, namely invasion and metastasis.

Confinement primes cells for faster migration by polarizing active mitochondria

Mechanical cues in the tumor microenvironment interplay with internal cellular processes to control cancer cell migration. Microscale pores present in tumor tissue confer varying degrees of confinement on migrating cells, increasing matrix contact and inducing cytoskeletal rearrangement. Previously, we observed that increased collagen matrix contact significantly increased cell migration speed and cell-induced strains within the matrix. However, the effects of this confinement on future cell migration are not fully understood. Here, we use a collagen microtrack platform to determine the effect of confinement on priming MDA-MB-231 cancer cells for fast migration. We show that migration through a confined track results in increased speed and accumulation of migratory machinery, including actin and active mitochondria, in the front of migrating breast cancer cells. By designing microtracks that allow cells to first navigate a region of high confinement, then a region of low confinement, we assessed whether migration in high confinement changes future migratory behavior. Indeed, cells maintain their speed attained in high confinement even after exiting to a region of low confinement, indicating that cells maintain memory of previous matrix cues to fuel fast migration. Active mitochondria maintain their location at the front of the cell even after cells leave high confinement. Furthermore, knocking out vinculin to disrupt focal adhesions disrupts active mitochondrial localization and disrupts the fast migration seen upon release from confinement. Together, these data suggest that active mitochondrial localization in confinement may facilitate fast migration post-confinement. By better understanding how confinement contributes to future cancer cell migration, we can identify potential therapeutic targets to inhibit breast cancer metastasis.

Molecular basis and cellular functions of vinculin-actin directional catch bonding

The ability of cells and tissues to respond differentially to mechanical forces applied in distinct directions is mediated by the ability of load-bearing proteins to preferentially maintain physical linkages in certain directions. However, the molecular basis and biological consequences of directional force-sensitive binding remain unclear. Vinculin (Vcn) is a load-bearing linker protein that exhibits directional catch bonding due to interactions between the Vcn tail domain (Vt) and filamentous (F)-actin. We developed a computational approach to predict Vcn residues involved in directional catch bonding and produced a set of associated Vcn variants with unaltered Vt structure, actin binding, or phospholipid interactions. Incorporation of the variants did not affect Vcn activation but reduced Vcn loading and altered exchange dynamics, consistent with the loss of directional catch bonding. Expression of Vcn variants perturbed the coordination of subcellular structures and cell migration, establishing key cellular functions for Vcn directional catch bonding.

Vinculin is essential for sustaining normal levels of endogenous forces at cell-cell contacts

Transmission of cell-generated (i.e., endogenous) tension at cell-cell contacts is crucial for tissue shape changes during morphogenesis and adult tissue repair in tissues such as epithelia. E-cadherin-based adhesions at cell-cell contacts are the primary means by which endogenous tension is transmitted between cells. The E-cadherin-β-catenin-α-catenin complex mechanically couples to the actin cytoskeleton (and thereby the cell's contractile machinery) both directly and indirectly. However, the key adhesion constituents required for substantial endogenous force transmission at these adhesions in cell-cell contacts are unclear. Due to the role of α-catenin as a mechanotransducer that recruits vinculin at cell-cell contacts, we expected α-catenin to be essential for sustaining normal levels of force transmission. Instead, using the traction force imbalance method to determine the inter-cellular force at a single cell-cell contact between cell pairs, we found that it is vinculin that is essential for sustaining normal levels of endogenous force transmission, with absence of vinculin decreasing the inter-cellular tension by over 50%. Our results constrain the potential mechanical pathways of force transmission at cell-cell contacts and suggest that vinculin can transmit forces at E-cadherin adhesions independent of α-catenin, possibly through β-catenin. Furthermore, we tested the ability of lateral cell-cell contacts to withstand external stretch and found that both vinculin and α-catenin are essential to maintain cell-cell contact stability under external forces.

Development of a Ratiometric Tension Sensor Exclusively Responding to Integrin Tension Magnitude in Live Cells

Integrin tensions are critical for cell mechanotransduction. By converting force to fluorescence, molecular tension sensors image integrin tensions in live cells with a high resolution. However, the fluorescence signal intensity results collectively from integrin tension magnitude, tension dwell time, integrin density, sensor accessibility, and so forth, making it highly challenging to specifically monitor the molecular force level of integrin tensions. Here, a ratiometric tension sensor (RTS) was developed to exclusively monitor the integrin tension magnitude. The RTS consists of two tension-sensing units that are coupled in series and always subject to the same integrin tension. These two units are activated by tension to fluoresce in separate spectra and with different activation rates. The ratio of their activation probabilities, reported by fluorescence ratiometric measurement, is solely determined by the local integrin tension magnitude. RTS responded sensitively to the variation of integrin tension magnitude in platelets and focal adhesions due to different cell plating times, actomyosin inhibition, or vinculin knockout. At last, RTS confirmed that integrin tension magnitude in platelets and focal adhesions decreases monotonically with the substrate rigidity, verifying the rigidity dependence of integrin tensions in live cells and suggesting that integrin tension magnitude could be a key biomechanical factor in cell rigidity sensing.

Cdk4 Regulates Glioblastoma Cell Invasion and Stemness and Is Target of a Notch Inhibitor Plus Resveratrol Combined Treatment

Glioblastoma multiforme (GBM) is one of the most aggressive types of cancer characterized by poor patient outcomes. To date, it is believed that the major cause of its recurrence and chemoresistance is represented by the enrichment of GBM stem cells (GSCs) sustained by the abnormal activation of a number of signaling pathways. In this study, we found that in GBM cells, treatment with low toxicity doses of the γ-secretase inhibitor RO4929097 (GSI), blocking the Notch pathway activity, in combination with resveratrol (RSV) was able to reverse the basal mesenchymal phenotype to an epithelial-like phenotype, affecting invasion and stemness interplay. The mechanism was dependent on cyclin D1 and cyclin-dependent kinase (CDK4), leading to a reduction of paxillin (Pxn) phosphorylation. Consequently, we discovered the reduced interaction of Pxn with vinculin (Vcl), which, during cell migration, transmits the intracellular forces to the extracellular matrix. The exogenous expression of a constitutively active Cdk4 mutant prevented the RSV + GSI inhibitory effects in GBM cell motility/invasion and augmented the expression of stemness-specific markers, as well as the neurosphere sizes/forming abilities in untreated cells. In conclusion, we propose that Cdk4 is an important regulator of GBM stem-like phenotypes and invasive capacity, highlighting how the combined treatment of Notch inhibitors and RSV could be prospectively implemented in the novel therapeutic strategies to target Cdk4 for these aggressive brain tumors.

Evaluation of focal adhesion mediated subcellular curvature sensing in response to engineered extracellular matrix

Fibril curvature is bioinstructive to attached cells. Similar to natural healthy tissues, an engineered extracellular matrix can be designed to stimulate cells to adopt desired phenotypes. To take full advantage of the curvature control in biomaterial fabrication methodologies, an understanding of the response to fibril subcellular curvature is required. In this work, we examined morphology, signaling, and function of human cells attached to electrospun nanofibers. We controlled curvature across an order of magnitude using nondegradable poly(methyl methacrylate) (PMMA) attached to a stiff substrate with flat PMMA as a control. Focal adhesion length and the distance of maximum intensity from the geographic center of the vinculin positive focal adhesion both peaked at a fiber curvature of 2.5 μm-1 (both ∼2× the flat surface control). Vinculin experienced slightly less tension when attached to nanofiber substrates. Vinculin expression was also more affected by a subcellular curvature than structural proteins α-tubulin or α-actinin. Among the phosphorylation sites we examined (FAK397, 576/577, 925, and Src416), FAK925 exhibited the most dependance on the nanofiber curvature. A RhoA/ROCK dependance of migration velocity across curvatures combined with an observation of cell membrane wrapping around nanofibers suggested a hybrid of migration modes for cells attached to fibers as has been observed in 3D matrices. Careful selection of nanofiber curvature for regenerative engineering scaffolds and substrates used to study cell biology is required to maximize the potential of these techniques for scientific exploration and ultimately improvement of human health.

Elevated Serum Vinculin in Patients with HBV/HCV-Associated Liver Cirrhosis and Hepatocellular Carcinoma: A Pilot Study

Background

The stiffness of the extracellular matrix (ECM) controls many cellular processes, such as migration and differentiation. Cells detect stiffness through adhesion structures termed focal adhesions (FAs). Vinculin, an actin-binding FA protein, plays a pivotal role in FA-mediated mechanotransduction.

Aim

This study aimed to explore the role of vinculin in the development of HBV/HCV-induced hepatocellular carcinoma (HCC).

Methods

Vinculin levels in a total number of 100 serum samples from patients with HBV/HCV-induced liver cirrhosis and HCC, as well as healthy controls, were analyzed using an enzyme-linked immunosorbent assay (ELISA).

Results

In patients with HCC and liver cirrhosis, the serum vinculin levels were significantly greater than in controls (503.8±242.2 and 728.4±1044.8 vs 77.7±36.1 respectively, p<0.001). However, results showed no link between serum vinculin and the clinicopathological features of HCC.

Conclusion

Patients with HBVor HCV-induced liver cirrhosis and HCC have significantly higher serum levels of vinculin than do controls. This might point to a potential role for vinculin in the development of HCC. More research into how this protein affects the development of HCC at the molecular level could lead to better clinical treatments and the development of new molecular therapies.

Elucidation of the Molecular Basis and Cellular Functions of Vinculin-Actin Directional Catch Bonding

The ability of cells and tissues to differentially resist or adapt to mechanical forces applied in distinct directions is mediated by the ability of load-bearing proteins to preferentially maintain physical linkages in certain directions. However, the molecular basis and biological consequences of directional force-sensitive binding are unclear. Vinculin (Vcn) is a load-bearing linker protein that exhibits directional catch bonding due to interactions between the Vcn tail domain (Vt) and filamentous (F)-actin. We developed a computational approach to predict Vcn residues involved in directional catch bonding and produced a set of associated Vcn variants with unaltered Vt structure, actin binding, or phospholipid interactions. Incorporation of these variants into Vcn biosensors did not perturb Vcn conformation, but reduced Vcn loading consistent with loss of directional catch bonding. Expression of Vcn variants perturbed the coalignment of FAs and F-actin and directed cell migration, establishing key cellular functions for Vcn directional catch bonding.

Vinculin transmits high-level integrin tensions that are dispensable for focal adhesion formation

Focal adhesions (FAs) transmit force and mediate mechanotransduction between cells and the matrix. Previous studies revealed that integrin-transmitted force is critical to regulate FA formation. As vinculin is a prominent FA protein implicated in integrin tension transmission, this work studies the relation among integrin tensions (force), vinculin (protein), and FA formation (structure) by integrin tension manipulation, force visualization and vinculin knockout (KO). Two DNA-based integrin tension tools are adopted: tension gauge tether (TGT) and integrative tension sensor (ITS), with TGT restricting integrin tensions under a designed Ttol (tension tolerance) value and ITS visualizing integrin tensions above the Ttol value by fluorescence. Results show that large FAs (area >1 μm2) were formed on the TGT surface with Ttol of 54 pN but not on those with lower Ttol values. Time-series analysis of FA formation shows that focal complexes (area <0.5 μm2) appeared on all TGT surfaces 20 min after cell plating, but only matured to large FAs on TGT with Ttol of 54 pN. Next, we tested FA formation in vinculin KO cells on TGT surfaces. Surprisingly, the Ttol value of TGT required for large FA formation is drastically decreased to 23 pN. To explore the cause, we visualized integrin tensions in both wild-type and vinculin KO cells using ITS. The results showed that integrin tensions in FAs of wild-type cells frequently activate ITS with Ttol of 54 pN. With vinculin KO, however, integrin tensions in FAs became lower and unable to activate 54 pN ITS. Force signal intensities of integrin tensions reported by 33 and 43 pN ITS were also significantly reduced with vinculin KO, suggesting that vinculin is essential to transmit high-level integrin tensions and involved in transmitting intermediate-level integrin tensions in FAs. However, the high-level integrin tensions transmitted by vinculin are not required by FA formation.

Moving through a changing world: Single cell migration in 2D vs. 3D

Migration of single adherent cells is frequently observed in the developing and adult organism and has been the subject of many studies. Yet, while elegant work has elucidated molecular and mechanical cues affecting motion dynamics on a flat surface, it remains less clear how cells migrate in a 3D setting. In this review, we explore the changing parameters encountered by cells navigating through a 3D microenvironment compared to cells crawling on top of a 2D surface, and how these differences alter subcellular structures required for propulsion. We further discuss how such changes at the micro-scale impact motion pattern at the macro-scale.

Tensin3 interaction with talin drives the formation of fibronectin-associated fibrillar adhesions

The formation of healthy tissue involves continuous remodeling of the extracellular matrix (ECM). Whilst it is known that this requires integrin-associated cell-ECM adhesion sites (CMAs) and actomyosin-mediated forces, the underlying mechanisms remain unclear. Here, we examine how tensin3 contributes to the formation of fibrillar adhesions (FBs) and fibronectin fibrillogenesis. Using BioID mass spectrometry and a mitochondrial targeting assay, we establish that tensin3 associates with the mechanosensors such as talin and vinculin. We show that the talin R11 rod domain binds directly to a helical motif within the central intrinsically disordered region (IDR) of tensin3, whilst vinculin binds indirectly to tensin3 via talin. Using CRISPR knock-out cells in combination with defined tensin3 mutations, we show (i) that tensin3 is critical for the formation of α5β1-integrin FBs and for fibronectin fibrillogenesis, and (ii) the talin/tensin3 interaction drives this process, with vinculin acting to potentiate it.

A Comprehensive Review on Collagen Type I Development of Biomaterials for Tissue Engineering: From Biosynthesis to Bioscaffold

Collagen is the most abundant structural protein found in humans and mammals, particularly in the extracellular matrix (ECM). Its primary function is to hold the body together. The collagen superfamily of proteins includes over 20 types that have been identified. Yet, collagen type I is the major component in many tissues and can be extracted as a natural biomaterial for various medical and biological purposes. Collagen has multiple advantageous characteristics, including varied sources, biocompatibility, sustainability, low immunogenicity, porosity, and biodegradability. As such, collagen-type-I-based bioscaffolds have been widely used in tissue engineering. Biomaterials based on collagen type I can also be modified to improve their functions, such as by crosslinking to strengthen the mechanical property or adding biochemical factors to enhance their biological activity. This review discusses the complexities of collagen type I structure, biosynthesis, sources for collagen derivatives, methods of isolation and purification, physicochemical characteristics, and the current development of collagen-type-I-based scaffolds in tissue engineering applications. The advancement of additional novel tissue engineered bioproducts with refined techniques and continuous biomaterial augmentation is facilitated by understanding the conventional design and application of biomaterials based on collagen type I.

Adhesive peptide and polymer density modulate 3D cell traction forces within synthetic hydrogels

Cell-extracellular matrix forces provide pivotal signals regulating diverse physiological and pathological processes. Although mechanobiology has been widely studied in two-dimensional configurations, limited research has been conducted in three-dimensional (3D) systems due to the complex nature of mechanics and cellular behaviors. In this study, we established a platform integrating a well-defined synthetic hydrogel system (PEG-4MAL) with 3D traction force microscopy (TFM) methodologies to evaluate deformation and force responses within synthetic microenvironments, providing insights that are not tractable using biological matrices because of the interdependence of biochemical and biophysical properties and complex mechanics. We dissected the contributions of adhesive peptide density and polymer density, which determines hydrogel stiffness, to 3D force generation for fibroblasts. A critical threshold of adhesive peptide density at a constant matrix elasticity is required for cells to generate 3D forces. Furthermore, matrix displacements and strains decreased with matrix stiffness whereas stresses, and tractions increased with matrix stiffness until reaching constant values at higher stiffness values. Finally, Rho-kinase-dependent contractility and vinculin expression are required to generate significant 3D forces in both collagen and synthetic hydrogels. This research establishes a tunable platform for the study of mechanobiology and provides new insights into how cells sense and transmit forces in 3D.

The focal adhesion protein β-parvin controls cardiomyocyte shape and sarcomere assembly in response to mechanical load

Physiological and pathological cardiac stress induced by exercise and hypertension, respectively, increase the hemodynamic load for the heart and trigger specific hypertrophic signals in cardiomyocytes leading to adaptive or maladaptive cardiac hypertrophy responses involving a mechanosensitive remodeling of the contractile cytoskeleton. Integrins sense load and have been implicated in cardiac hypertrophy, but how they discriminate between the two types of cardiac stress and translate mechanical loads into specific cytoskeletal signaling pathways is not clear. Here, we report that the focal adhesion protein β-parvin is highly expressed in cardiomyocytes and facilitates the formation of cell protrusions, the serial assembly of newly synthesized sarcomeres, and the hypertrophic growth of neonatal rat ventricular cardiomyocytes (NRVCs) in vitro. In addition, physiological mechanical loading of NRVCs by either the application of cyclic, uni-axial stretch, or culture on physiologically stiff substrates promotes NRVC elongation in a β-parvin-dependent manner, which is achieved by binding of β-parvin to α/β-PIX, which in turn activates Rac1. Importantly, loss-of-function studies in mice also revealed that β-parvin is essential for the exercise-induced cardiac hypertrophy response in vivo. Our results identify β-parvin as a novel mechano-responsive signaling hub in hypertrophic cardiomyocytes that drives cell elongation in response to physiological mechanical loads.

Actomyosin contractility requirements and reciprocal cell-tissue mechanics for cancer cell invasion through collagen-based channels

The interstitial tumor microenvironment is composed of heterogeneously organized collagen-rich porous networks as well as channel-like structures and interfaces which provide both barriers and guidance for invading cells. Tumor cells invading 3D random porous collagen networks depend upon actomyosin contractility to deform and translocate the nucleus, whereas Rho/Rho-associated kinase-dependent contractility is largely dispensable for migration in stiff capillary-like confining microtracks. To investigate whether this dichotomy of actomyosin contractility dependence also applies to physiological, deformable linear collagen environments, we developed nearly barrier-free collagen-scaffold microtracks of varying cross section using two-photon laser ablation. Both very narrow and wide tracks supported single-cell migration by either outward pushing of collagen up to four times when tracks were narrow, or cell pulling on collagen walls down to 50% of the original diameter by traction forces of up to 40 nN when tracks were wide, resulting in track widths optimized to single-cell diameter. Targeting actomyosin contractility by synthetic inhibitors increased cell elongation and nuclear shape change in narrow tracks and abolished cell-mediated deformation of both wide and narrow tracks. Accordingly, migration speeds in all channel widths reduced, with migration rates of around 45-65% of the original speed persisting. Together, the data suggest that cells engage actomyosin contraction to reciprocally adjust both own morphology and linear track width to optimal size for effective cellular locomotion.

VE-cadherin enables trophoblast endovascular invasion and spiral artery remodeling during placental development

During formation of the mammalian placenta, trophoblasts invade the maternal decidua and remodel spiral arteries to bring maternal blood into the placenta. This process, known as endovascular invasion, is thought to involve the adoption of functional characteristics of vascular endothelial cells (ECs) by trophoblasts. The genetic and molecular basis of endovascular invasion remains poorly defined, however, and whether trophoblasts utilize specialized endothelial proteins in an analogous manner to create vascular channels remains untested. Vascular endothelial (VE-)cadherin is a homotypic adhesion protein that is expressed selectively by ECs in which it enables formation of tight vessels and regulation of EC junctions. VE-cadherin is also expressed in invasive trophoblasts and is a prime candidate for a molecular mechanism of endovascular invasion by those cells. Here, we show that VE-cadherin is required for trophoblast migration and endovascular invasion into the maternal decidua in the mouse. VE-cadherin deficiency results in loss of spiral artery remodeling that leads to decreased flow of maternal blood into the placenta, fetal growth restriction, and death. These studies identify a non-endothelial role for VE-cadherin in trophoblasts during placental development and suggest that endothelial proteins may play functionally unique roles in trophoblasts that do not simply mimic those in ECs.

A Protein Composite Neural Scaffold Modulates Astrocyte Migration and Transcriptome Profile

Bioscaffold implantation is a promising approach to facilitate the repair and regeneration of wounded neural tissue after injury to the spinal cord or peripheral nerves. However, such bioscaffold grafts currently result in only limited functional recovery. The generation of a neural scaffold using a combination of collagen and glutenin is reported. The conduit material and mechanical properties, as well as its effect on astrocyte behavior is tested. After neural injuries, astrocytes move into the lesion and participate in the process of remodeling the micro-architecture of the wounded neural tissue. In this study, human astrocytes grown on glutenin-collagen scaffolds show higher motility and a lower proliferation rate compared with those grown on collagen scaffolds. RNA sequencing reveals that astrocytes grown on the two types of scaffolds show differentially expressed genes in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways such as actin cytoskeleton and focal adhesion that regulate astrocyte migration on scaffolds. The gene expression of aggrecan and versican, chondroitin sulfate proteoglycans that inhibit axonal growth, is down-regulated in astrocytes grown on glutenin-collagen scaffolds. These outcomes indicate that the implantation of glutenin-collagen scaffolds may promote astrocyte function in the neural regeneration process by enhanced cell migration and reduced glial scar formation.

The C-terminal actin-binding domain of talin forms an asymmetric catch bond with F-actin

Talin is a mechanosensitive adaptor protein that links integrins to the actin cytoskeleton at cell–extracellular matrix adhesions. Although the C-terminal actin-binding domain ABS3 of talin is required for function, it binds weakly to actin in solution. We show that ABS3 binds actin strongly only when subjected to mechanical forces comparable to those generated by the cytoskeleton. Moreover, the interaction between ABS3 and actin depends strongly on the direction of force in a manner predicted to organize actin to facilitate adhesion growth and efficient cytoskeletal force generation. These characteristics can explain how force sensing by talin helps to nucleate adhesions precisely when and where they are required to transmit force between the cytoskeleton and the extracellular matrix.

Focal adhesions (FAs) are large, integrin-based protein complexes that link cells to the extracellular matrix (ECM). FAs form only when and where they are necessary to transmit force between the cellular cytoskeleton and the ECM, but how this occurs remains poorly understood. Talin is a 270-kDa adaptor protein that links integrins to filamentous (F)-actin and recruits additional components during FA assembly in a force-dependent manner. Cell biological and developmental data demonstrate that the third and C-terminal F-actin–binding site (ABS3) of talin is required for normal FA formation. However, purified ABS3 binds F-actin only weakly in solution. We used a single molecule optical trap assay to examine how and whether ABS3 binds F-actin under physiologically relevant mechanical loads. We find that ABS3 forms a catch bond with F-actin when force is applied toward the pointed end of the actin filament, with binding lifetimes >100-fold longer than when force is applied toward the barbed end. Long-lived bonds to F-actin under load require the ABS3 C-terminal dimerization domain, whose cleavage has been reported to regulate FA turnover. Our results support a mechanism in which talin ABS3 preferentially binds to and orients actin filaments with barbed ends facing the cell periphery, thus nucleating long-range order in the actin cytoskeleton. We suggest that talin ABS3 may function as a molecular AND gate that allows FA growth only when sufficient integrin density, F-actin polarization, and mechanical tension are simultaneously present.

Complete Model of Vinculin Suggests the Mechanism of Activation by Helical Super-Bundle Unfurling

To shed light onto the activation mechanism of vinculin, we carried out a detailed refinement of chicken vinculin and compared it to the human protein which is greater than 95% identical. Refinement resulted in a complete and significantly improved model. This model includes important elements such as a pro-rich strap region (PRR) and C-terminus. The conformation of the PRR stabilized by its inter- and intra-molecular contacts shows a dynamic, but relatively stable motif that constitutes a docking platform for multiple molecules. The contact of the C-terminus with the PRR suggests that phosphorylation of Tyr1065 might control activation and membrane binding. Improved electron densities showed the presence of large solvent molecules such as phosphates/sulfates and a head-group of PIP2. The improved model allowed for a computational stability analysis to be performed by the program Corex/Best which located numerous hot-spots of increased and decreased stability. Proximity of the identified binding sites for regulatory partners involved in inducing or suppressing the activation of vinculin to the unstable elements sheds new light onto the activation pathway and differential activation. This stability analysis suggests that the activation pathway proceeds by unfurling of the super-bundle built from four bundles of helices without separation of the Vt region (840-1066) from the head. According to our mechanism, when activating proteins bind at the strap region a separation of N and C terminal bundles occurs, followed by unfurling of the super-bundle and flattening of the general shape of the molecule, which exposes the interaction sites for binding of auxiliary proteins.

DEHP mediates drug resistance by directly targeting AhR in human breast cancer

Resistance to chemotherapy and hormonal therapy is a major clinical problem in breast cancer medicine, especially for cancer metastasis and recurrence. Di(2-ethylhexyl)phthalate (DEHP) affects drug resistance by an unknown mechanism of action. Here we analyzed breast cancer patients (N = 457) and found that Σ₄MEHP (the sum of MEHP, MEHHP, MECPP and MEOHP concentrations) in urine was significantly higher (P = 0.018) in the recurrent breast cancer group compared with non-recurrent patients. Σ₄MEHP-High was positively and significantly correlated with tumor stage (P = 0.005), lymph node status (P = 0.001), estrogen receptor status (P = 0.010), Her2/Neu status (P = 0.004), recurrence (P = 0.000) and tumor size (P = 0.002), as well as an independent prognostic marker (OR = 1.868; 95% CI = 1.424-2.451; P < 0.000) associated with poor survival rates based on a positive Her2/Neu status (P = 0.035). In addition, we found that DEHP inhibited paclitaxel and doxorubicin effects in breast cancer cell lines MCF-7 and MDA-MB-231 and in zebrafish and mouse tumor initiation models. DEHP induced trefoil factor 3 (TFF3) expression through the vinculin/aryl hydrocarbon receptor (AhR)/ERK signaling pathway and induced CYP2D6, CYP2C8 and CYP3A4 expression through the AhR genomic pathway to increase the epithelial-mesenchymal transition (EMT) and doxorubicin metabolism, respectably. DEHP mediated AhR-related alterations in estrogen receptor expression through the ubiquitination system, which decreased tamoxifen effects in AhR knockout mice. These findings suggest a novel therapeutic avenue by targeting AhR in drug-resistant and recurrent breast cancer.

Stage-dependent function of Wnt5a during male external genitalia development

External genitalia development in mice involves multiple developmental processes under the regulation of various signaling pathways. Wnt5a, one of the major Wnt ligands, is a crucial developmental regulator of outgrowing organs such as the limb, the mandible, and the external genitalia. Defects in Wnt5a signaling have been linked to Robinow syndrome, a genetic disorder in which male patients manifest a micropenis and defective urethral tube formation. Whereas Wnt5a is required for cell proliferation during embryonic external genitalia outgrowth, its role for urethral tube formation has yet to be understood. Here, we show that Wnt5a contributes to urethral tube formation as well as external genitalia outgrowth. Wnt5a is expressed in the embryonic external genitalia mesenchyme, and mesenchymal-specific conditional Wnt5a knockout mice resulted in hypospadias-like urethral defects. Early deletion of Wnt5a at E10.5 showed severe defects in both external genitalia outgrowth and urethral tube formation, along with reduced cell proliferation. The severe urethral tube defect persisted during later timing deletion of Wnt5a (E13.5). Further analyses revealed that loss of Wnt5a disrupted cell polarity and led to a reduction of the phosphorylated myosin light chain and the focal adhesion protein, vinculin. Altogether, these results suggest that Wnt5a coordinates cell proliferation and directed cell migration in a stage-dependent manner during male external genitalia development. Furthermore, Wnt5a may regulate cell polarity, focal adhesion formation, and cell contractility, leading to directed cell migration during male-type urethral formation in a manner that has not been reported in other organ fusion events.

In vitro stimulation with radiofrequency currents promotes proliferation and migration in human keratinocytes and fibroblasts

Capacitive-resistive electric transfer (CRET) therapies have been proposed as strategies for regeneration of cutaneous tissue lesions. Previous studies by our group have shown that intermittent stimulation with 448 kHz CRET currents at subthermal densities promotes in vitro proliferation of human stem cells involved in tissue regeneration. The present study investigates the effects of the in vitro exposure to these radiofrequency (RF) currents on the proliferation and migration of keratinocytes and fibroblasts, the main cell types involved in skin regeneration. The effects of the electric stimulation on cell proliferation and migration were studied through XTT and wound closure assays, respectively. The CRET effects on the expression and location of proteins involved in proliferation and migration were assessed by immunoblot and immunofluorescence. The obtained results reveal that electrostimulation promotes proliferation and/or migration in keratinocytes and fibroblasts. These effects would be mediated by changes observed in the expression and location of intercellular adhesion proteins such as β-catenin and E-cadherin, of proteins involved in cell-to-substrate adhesion such as vinculin, p-FAK and the metalloproteinase MMP-9, and of other proteins that control both processes: MAP kinases p-p38, p-JUNK and p-ERK1/2. These responses could represent a mechanism underlying the promotion of normotrophic wound regeneration induced by CRET. Indeed, electric stimulation would favor completion of granulation tissue formation prior to the closure of the outer tissue layers, thus preventing abnormal wound cicatrization or chronification.

Bioinspired peptide adhesion on Ti implants alleviates wear particle-induced inflammation and improves interfacial osteogenesis

In the inflammatory peri-implant microenvironment, excessive polarization of macrophages to the proinflammatory M1 phenotype can trigger the secretion of inflammatory cytokines, which promote bone resorption and impede osteogenesis around implants. The direct consequence of this process is the failure of prosthetic implants due to aseptic loosening. To reverse the inflammatory microenvironment and prevent prosthesis loosening, a mussel adhesion-inspired surface strategy was used for bioengineering of titanium implants with integrin-binding ability. In our design, a mussel-inspired catecholic peptide with tetravalent 3,4-dihydroxy-l-phenylalanine (DOPA) and Arg-Gly-Asp (RGD) sequences was synthesized. The peptide can easily anchor to the surface of medical titanium materials through a mussel adhesive mechanism. We found that peptide-decorated titanium implants could effectively inhibit peri-implant inflammation in a wear particle model and could promote the polarization of macrophages to a pro-healing M2 phenotype by interfering with integrin-α₂β₁ and integrin-α_vβ₃. Moreover, the peptide coating increased the adherence of osteoblasts and promoted osteogenesis on titanium implants even under inflammatory conditions. This work suggested that this biomimetic catecholic integrin-binding peptide can provide facile tactics for surface bioengineering of medical prostheses with improved interfacial osteogenesis under inflammatory conditions, which might contribute greatly to the prevention of prosthesis loosening and the improvement of clinical outcomes.

Alkaloid and acetogenin-rich fraction from Annona crassiflora fruit peel inhibits proliferation and migration of human liver cancer HepG2 cells

Plant species from Annonaceae are commonly used in traditional medicine to treat various cancer types. This study aimed to investigate the antiproliferative potential of an alkaloid and acetogenin-rich fraction from the fruit peel of Annona crassiflora in HepG2 cells. A liquid-liquid fractionation was carried out on the ethanol extract of A. crassiflora fruit peel in order to obtain an alkaloid and acetogenin-rich fraction (AF-Ac). Cytotoxicity, proliferation and migration were evaluated in the HepG2 cells, as well as the proliferating cell nuclear antigen (PCNA), vinculin and epidermal growth factor receptor (EGFR) expression. In addition, intracellular Ca2+ was determined using Fluo4-AM and fluorescence microscopy. First, 9 aporphine alkaloids and 4 acetogenins that had not yet been identified in the fruit peel of A. crassiflora were found in AF-Ac. The treatment with 50 μg/mL AF-Ac reduced HepG2 cell viability, proliferation and migration (p < 0.001), which is in accordance with the reduced expression of PCNA and EGFR levels (p < 0.05). Furthermore, AF-Ac increased intracellular Ca2+ in the HepG2 cells, mobilizing intracellular calcium stores, which might be involved in the anti-migration and anti-proliferation capacities of AF-Ac. Our results support the growth-inhibitory potential of AF-Ac on HepG2 cells and suggest that this effect is triggered, at least in part, by PCNA and EGFR modulation and mobilization of intracellular Ca2+. This study showed biological activities not yet described for A. crassiflora fruit peel, which provide new possibilities for further in vivo studies to assess the antitumoral potential of A. crassiflora, especially its fruit peel.

Scaffolds from Self-Assembling Tetrapeptides Support 3D Spreading, Osteogenic Differentiation, and Angiogenesis of Mesenchymal Stem Cells

The apparent rise of bone disorders demands advanced treatment protocols involving tissue engineering. Here, we describe self-assembling tetrapeptide scaffolds for the growth and osteogenic differentiation of human mesenchymal stem cells (hMSCs). The rationally designed peptides are synthetic amphiphilic self-assembling peptides composed of four amino acids that are nontoxic. These tetrapeptides can quickly solidify to nanofibrous hydrogels that resemble the extracellular matrix and provide a three-dimensional (3D) environment for cells with suitable mechanical properties. Furthermore, we can easily tune the stiffness of these peptide hydrogels by just increasing the peptide concentration, thus providing a wide range of peptide hydrogels with different stiffnesses for 3D cell culture applications. Since successful bone regeneration requires both osteogenesis and vascularization, our scaffold was found to be able to promote angiogenesis of human umbilical vein endothelial cells (HUVECs) in vitro. The results presented suggest that ultrashort peptide hydrogels are promising candidates for applications in bone tissue engineering.

The Measurement and Analysis of Impedance Response of HeLa Cells to Distinct Chemotherapy Drugs

Electric cell–substrate impedance sensing exhibits a real-time and label-free feature to monitor the response of cells stimulated by various biochemical and mechanical signals. Alterations in the currents passing through the cell–electrode system characterize the impedance variations of cells. The impedance responses of HeLa cells under distinct chemotherapy drugs combine the effects of cell proliferation and cell–substrate adhesion. Optimal interdigitated electrodes were selected to explore the impedance responses of HeLa cells. Measurements of impedance of cells in response to three widely used chemotherapy drugs in clinical practice, namely cisplatin, doxorubicin, 5-fluorouracil, were performed. The results demonstrated that distinct impedance responses of HeLa cells to drugs were exhibited and a decrease in measured impedance was observed after drug treatment, accompanied by alterations in the distribution and intensity of the adhesion-related protein vinculin and the rate of cell proliferation. The link between the impedance profiles of HeLa cells and their biological functions was developed based on the circuit model. This study demonstrated the weights of cell proliferation and adhesion of HeLa cells under the treatments of DDP, DOX, and 5-FU, resulted in distinct impedance responses of cells, providing an impedance-based evaluation methodology for cervical cancer treatment.

Manipulation of Focal Adhesion Signaling by Pathogenic Microbes

Focal adhesions (FAs) serve as dynamic signaling hubs within the cell. They connect intracellular actin to the extracellular matrix (ECM) and respond to environmental cues. In doing so, these structures facilitate important processes such as cell-ECM adhesion and migration. Pathogenic microbes often modify the host cell actin cytoskeleton in their pursuit of an ideal replicative niche or during invasion to facilitate uptake. As actin-interfacing structures, FA dynamics are also intimately tied to actin cytoskeletal organization. Indeed, exploitation of FAs is another avenue by which pathogenic microbes ensure their uptake, survival and dissemination. This is often achieved through the secretion of effector proteins which target specific protein components within the FA. Molecular mimicry of the leucine-aspartic acid (LD) motif or vinculin-binding domains (VBDs) commonly found within FA proteins is a common microbial strategy. Other effectors may induce post-translational modifications to FA proteins through the regulation of phosphorylation sites or proteolytic cleavage. In this review, we present an overview of the regulatory mechanisms governing host cell FAs, and provide examples of how pathogenic microbes have evolved to co-opt them to their own advantage. Recent technological advances pose exciting opportunities for delving deeper into the mechanistic details by which pathogenic microbes modify FAs.

Physical limits to sensing material properties

All materials respond heterogeneously at small scales, which limits what a sensor can learn. Although previous studies have characterized measurement noise arising from thermal fluctuations, the limits imposed by structural heterogeneity have remained unclear. In this paper, we find that the least fractional uncertainty with which a sensor can determine a material constant λ0 of an elastic medium is approximately [Formula: see text] for a ≫ d ≫ ξ, [Formula: see text], and D > 1, where a is the size of the sensor, d is its spatial resolution, ξ is the correlation length of fluctuations in λ0, Δλ is the local variability of λ0, and D is the dimension of the medium. Our results reveal how one can construct devices capable of sensing near these limits, e.g. for medical diagnostics. We use our theoretical framework to estimate the limits of mechanosensing in a biopolymer network, a sensory process involved in cellular behavior, medical diagnostics, and material fabrication.

Paxillin family of focal adhesion adaptor proteins and regulation of cancer cell invasion

The paxillin family of proteins, including paxillin, Hic-5, and leupaxin, are focal adhesion adaptor/scaffolding proteins which localize to cell-matrix adhesions and are important in cell adhesion and migration of both normal and cancer cells. Historically, the role of these proteins in regulating the actin cytoskeleton through focal adhesion-mediated signaling has been well documented. However, studies in recent years have revealed additional functions in modulating the microtubule and intermediate filament cytoskeletons to affect diverse processes including cell polarization, vesicle trafficking and mechanosignaling. Expression of paxillin family proteins in stromal cells is also important in regulating tumor cell migration and invasion through non-cell autonomous effects on the extracellular matrix. Both paxillin and Hic-5 can also influence gene expression through a variety of mechanisms, while their own expression is frequently dysregulated in various cancers. Accordingly, these proteins may serve as valuable targets for novel diagnostic and treatment approaches in cancer.

Actomyosin-dependent invasion of endothelial sprouts in collagen

During sprouting angiogenesis-the growth of blood vessels from the existing vasculature-endothelial cells (ECs) adopt an elongated invasive form and exert forces at cell-cell and cell-matrix interaction sites. These cell shape changes and cellular tractions require extensive reorganizations of the actomyosin network. However, the respective roles of actin and myosin for endothelial sprouting are not fully elucidated. In this study, we further investigate these roles by treating 2D-migrating and 3D-sprouting ECs with chemical compounds targeting either myosin or actin. These treatments affected the endothelial cytoskeleton drastically and reduced the invasive response in a compound-specific manner; pointing toward a tight control of the actin and myosin activity during sprouting. Clusters in the data further illustrate that endothelial sprout morphology is sensitive to the in vitro model mechanical microenvironment and directs future research toward mechanical substrate guidance as a strategy for promoting engineered tissue vascularization. In summary, our results add to a growing corpus of research highlighting a key role of the cytoskeleton for sprouting angiogenesis.

Conditioned medium from the human umbilical cord-mesenchymal stem cells stimulate the proliferation of human keratinocytes

OBJECTIVES

Wound healing is a complex process with a sequence of restoring and inhibition events such as cell proliferation, differentiation, migration as well as adhesion. Mesenchymal stem cells (MSC) derived conditioned medium (CM) has potent therapeutic functions and promotes cell proliferation, anti-oxidant, immunosuppressive, and anti-apoptotic effects. The main aim of this research is to study the role of human umbilical cord-mesenchymal stem cells (UC-MSCs) derived CM in stimulating the proliferation of human keratinocytes (HaCaT).

METHODS

Firstly, MSC were isolated from human umbilical cords (UC) and the cells were then cultured in proliferative medium. We prepared and collected the CM after 72 h. Morphological changes were observed after the treatment of HaCaT cells with CM. To validate the findings, proliferation rate, clonal efficiency and also gene expression studies were performed.

RESULTS

Increased proliferation rate was observed and confirmed with the expression of Proliferating Cell Nuclear Antigen (PCNA) after treatment with HaCaT cells. Cell-cell strap formation was also observed when HaCaT cells were treated with CM for a period of 5-6 days which was confirmed by the increased expression of Collagen Type 1 Alpha 1 chain (Col1A1).

CONCLUSIONS

Our results from present study depicts that the secretory components in the CM might play a significant role by interacting with keratinocytes to promote proliferation and migration. Thus, the CM stimulates cellular proliferation, epithelialization and migration of skin cells which might be the future promising application in wound healing.

Effect of Nuclear Stiffness on Cell Mechanics and Migration of Human Breast Cancer Cells

The migration and invasion of cancer cells through 3D confined extracellular matrices is coupled to cell mechanics and the mechanics of the extracellular matrix. Cell mechanics is mainly determined by both the mechanics of the largest organelle in the cell, the nucleus, and the cytoskeletal architecture of the cell. Hence, cytoskeletal and nuclear mechanics are the major contributors to cell mechanics. Among other factors, steric hindrances of the extracellular matrix confinement are supposed to affect nuclear mechanics and thus also influence cell mechanics. Therefore, we propose that the percentage of invasive cells and their invasion depths into loose and dense 3D extracellular matrices is regulated by both nuclear and cytoskeletal mechanics. In order to investigate the effect of both nuclear and cytoskeletal mechanics on the overall cell mechanics, we firstly altered nuclear mechanics by the chromatin de-condensing reagent Trichostatin A (TSA) and secondly altered cytoskeletal mechanics by addition of actin polymerization inhibitor Latrunculin A and the myosin inhibitor Blebbistatin. In fact, we found that TSA-treated MDA-MB-231 human breast cancer cells increased their invasion depth in dense 3D extracellular matrices, whereas the invasion depths in loose matrices were decreased. Similarly, the invasion depths of TSA-treated MCF-7 human breast cancer cells in dense matrices were significantly increased compared to loose matrices, where the invasion depths were decreased. These results are also valid in the presence of a matrix-metalloproteinase inhibitor GM6001. Using atomic force microscopy (AFM), we found that the nuclear stiffnesses of both MDA-MB-231 and MCF-7 breast cancer cells were pronouncedly higher than their cytoskeletal stiffness, whereas the stiffness of the nucleus of human mammary epithelial cells was decreased compared to their cytoskeleton. TSA treatment reduced cytoskeletal and nuclear stiffness of MCF-7 cells, as expected. However, a softening of the nucleus by TSA treatment may induce a stiffening of the cytoskeleton of MDA-MB-231 cells and subsequently an apparent stiffening of the nucleus. Inhibiting actin polymerization using Latrunculin A revealed a softer nucleus of MDA-MB-231 cells under TSA treatment. This indicates that the actin-dependent cytoskeletal stiffness seems to be influenced by the TSA-induced nuclear stiffness changes. Finally, the combined treatment with TSA and Latrunculin A further justifies the hypothesis of apparent nuclear stiffening, indicating that cytoskeletal mechanics seem to be regulated by nuclear mechanics.

Ovarian Cancer Exosomes Trigger Differential Biophysical Response in Tumor-Derived Fibroblasts

Exosomes are cell-secreted microvesicles that play important roles in epithelial ovarian cancer (EOC) progression, as they are constantly secreted into ascites fluids. While cells spontaneously release exosomes, alterations in intracellular calcium or extracellular pH can release additional exosomes. Yet, little is known about how these exosomes compare to those that are continuously released without stimulation and how they mediate cellular activities important in cancer progression. Here, we demonstrate that chelation of extracellular calcium leads to release of chelation-induced exosomes (CI-exosomes) from OVCAR-3 EOC cells. CI-exosomes display a unique miRNA profile compared to naturally secreted exosomes (SEC-exosomes). Furthermore, treatment with CI- and SEC-exosomes leads to differential biophysical and functional changes including, adhesion and migration in EOC-derived fibroblasts that suggest the development of a malignant tumor microenvironment. This result highlights how tumor environmental factors contribute to heterogeneity in exosome populations and how different exosome populations mediate diversity in stromal cell behavior.

Highly durable crack sensor integrated with silicone rubber cantilever for measuring cardiac contractility

To date, numerous biosensing platforms have been developed for assessing drug-induced cardiac toxicity by measuring the change in contractile force of cardiomyocytes. However, these low sensitivity, low-throughput, and time-consuming processes are severely limited in their real-time applications. Here, we propose a cantilever device integrated with a polydimethylsiloxane (PDMS)-encapsulated crack sensor to measure cardiac contractility. The crack sensor is chemically bonded to a PDMS thin layer that allows it to be operated very stably in culture media. The reliability of the proposed crack sensor has been improved dramatically compared to no encapsulation layer. The highly sensitive crack sensor continuously measures the cardiac contractility without changing its gauge factor for up to 26 days (>5 million heartbeats), while changes in contractile force induced by drugs are monitored using the crack sensor-integrated cantilever. Finally, experimental results are compared with those obtained via conventional optical methods to verify the feasibility of building a contraction-based drug-toxicity testing system.

Measuring cardiac contractility is challenging. Here, the authors encapsulated a crack-based sensor with polydimethylsiloxane, thereby endowing the sensor with the stability to measure cardiac contractility for up to 26 days as well as monitoring drug-induced cardiac toxicity in cell culture.

The use of mixed collagen-Matrigel matrices of increasing complexity recapitulates the biphasic role of cell adhesion in cancer cell migration: ECM sensing, remodeling and forces at the leading edge of cancer invasion

The migration of cancer cells is highly regulated by the biomechanical properties of their local microenvironment. Using 3D scaffolds of simple composition, several aspects of cancer cell mechanosensing (signal transduction, EMC remodeling, traction forces) have been separately analyzed in the context of cell migration. However, a combined study of these factors in 3D scaffolds that more closely resemble the complex microenvironment of the cancer ECM is still missing. Here, we present a comprehensive, quantitative analysis of the role of cell-ECM interactions in cancer cell migration within a highly physiological environment consisting of mixed Matrigel-collagen hydrogel scaffolds of increasing complexity that mimic the tumor microenvironment at the leading edge of cancer invasion. We quantitatively show that the presence of Matrigel increases hydrogel stiffness, which promotes β1 integrin expression and metalloproteinase activity in H1299 lung cancer cells. Then, we show that ECM remodeling activity causes matrix alignment and compaction that favors higher tractions exerted by the cells. However, these traction forces do not linearly translate into increased motility due to a biphasic role of cell adhesions in cell migration: at low concentration Matrigel promotes migration-effective tractions exerted through a high number of small sized focal adhesions. However, at high Matrigel concentration, traction forces are exerted through fewer, but larger focal adhesions that favor attachment yielding lower cell motility.

The E3 ligase MuRF2 plays a key role in the functional capacity of skeletal muscle fibroblasts

Fibroblasts are a highly heterogeneous population of cells, being found in a large number of different tissues. These cells produce the extracellular matrix, which is essential to preserve structural integrity of connective tissues. Fibroblasts are frequently engaged in migration and remodeling, exerting traction forces in the extracellular matrix, which is crucial for matrix deposition and wound healing. In addition, previous studies performed on primary myoblasts suggest that the E3 ligase MuRF2 might function as a cytoskeleton adaptor. Here, we hypothesized that MuRF2 also plays a functional role in skeletal muscle fibroblasts. We found that skeletal muscle fibroblasts express MuRF2 and its siRNA knock-down promoted decreased fibroblast migration, cell border accumulation of polymerized actin, and down-regulation of the phospho-Akt expression. Our results indicated that MuRF2 was necessary to maintain the actin cytoskeleton functionality in skeletal muscle fibroblasts via Akt activity and exerted an important role in extracellular matrix remodeling in the skeletal muscle tissue.

Proteomic Analysis Reveals Anti-Fibrotic Effects of Blue Light Photobiomodulation on Fibroblasts

BACKGROUND AND OBJECTIVES

This study was aimed at determining the effects of blue light photobiomodulation on primary adult mouse dermal fibroblasts (AMDFs) and the associated signaling pathways.

STUDY DESIGN/MATERIALS AND METHODS

Cultured AMDFs from adult C57BL/6 mice were irradiated by blue light from a light-emitting diode (wavelength = 463 ± 50 nm; irradiance = 5 mW/cm² ; energy density = 4-8 J/cm² ). The cells were analyzed using mass spectrometry for proteomics/phosphoproteomics, AlamarBlue assay for mitochondrial activity, time-lapse video for cell migration, quantitative polymerase chain reaction for gene expression, and immunofluorescence for protein expression.

RESULTS

Proteomic/phosphoproteomic analysis showed inhibition of extracellular signal-regulated kinases/mammalian target of rapamycin and casein kinase 2 pathways, cell motility-related networks, and multiple metabolic processes, including carbon metabolism, biosynthesis of amino acid, glycolysis/gluconeogenesis, and the pentose phosphate pathway. Functional analysis demonstrated inhibition of mitochondrial activities, cell migration, and mitosis. Expression of growth promoting insulin-like growth factor 1 and fibrosis-related genes, including transforming growth factor β1 (TGFβ1) and collagen type 1 ɑ2 chain diminished. Protein expression of α-smooth muscle actin, an important regulator of myofibroblast functions, was also suppressed.

CONCLUSIONS

Low-level blue light exerted suppressive effects on AMDFs, including suppression of mitochondrial activity, metabolism, cell motility, proliferation, TGFβ1 levels, and collagen I production. Low-level blue light can be a potential treatment for the prevention and reduction of tissue fibrosis, such as hypertrophic scar and keloids. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Myosin IIA-mediated forces regulate multicellular integrity during vascular sprouting

Angiogenic sprouting is a critical process involved in vascular network formation within tissues. During sprouting, tip cells and ensuing stalk cells migrate collectively into the extracellular matrix while preserving cell–cell junctions, forming patent structures that support blood flow. Although several signaling pathways have been identified as controlling sprouting, it remains unclear to what extent this process is mechanoregulated. To address this question, we investigated the role of cellular contractility in sprout morphogenesis, using a biomimetic model of angiogenesis. Three-dimensional maps of mechanical deformations generated by sprouts revealed that mainly leader cells, not stalk cells, exert contractile forces on the surrounding matrix. Surprisingly, inhibiting cellular contractility with blebbistatin did not affect the extent of cellular invasion but resulted in cell–cell dissociation primarily between tip and stalk cells. Closer examination of cell–cell junctions revealed that blebbistatin impaired adherens-junction organization, particularly between tip and stalk cells. Using CRISPR/Cas9-mediated gene editing, we further identified NMIIA as the major isoform responsible for regulating multicellularity and cell contractility during sprouting. Together, these studies reveal a critical role for NMIIA-mediated contractile forces in maintaining multicellularity during sprouting and highlight the central role of forces in regulating cell–cell adhesions during collective motility.

Inactivation of Lgi1 in murine neuronal precursor cells leads to dysregulation of axon guidance pathways

LGI1 mutations predispose to a rare epilepsy syndrome and when inactivated in mice leads to early onset seizures and premature death. Histopathology of the mature brain soon after birth shows cortical dysplasia in Lgi1 null mice with hypercellularity in the outer cortical layers. Here we show extensive gene expression changes in neuronal precursor cells from Lgi1 null mice compared with wild type mice. The most significantly dysregulated pathway involves canonical axon guidance signaling with multiple networks involved in cell movement, adhesion and invasion related to actin cytoskeleton reorganization. The Lgi1 null NPCs show increased cell motility in vitro compared with normal counterparts. Dysregulation of genes critical to cell movement/migration and critical transcription factors involved in early neuronal development is a prominent feature. These studies provide a critical mechanistic link to the observation of increased cellularity in the outer layers of the developing cortex in Lgi1 null mice.

FluoroCellTrack: An algorithm for automated analysis of high-throughput droplet microfluidic data

High-throughput droplet microfluidic devices with fluorescence detection systems provide several advantages over conventional end-point cytometric techniques due to their ability to isolate single cells and investigate complex intracellular dynamics. While there have been significant advances in the field of experimental droplet microfluidics, the development of complementary software tools has lagged. Existing quantification tools have limitations including interdependent hardware platforms or challenges analyzing a wide range of high-throughput droplet microfluidic data using a single algorithm. To address these issues, an all-in-one Python algorithm called FluoroCellTrack was developed and its wide-range utility was tested on three different applications including quantification of cellular response to drugs, droplet tracking, and intracellular fluorescence. The algorithm imports all images collected using bright field and fluorescence microscopy and analyzes them to extract useful information. Two parallel steps are performed where droplets are detected using a mathematical Circular Hough Transform (CHT) while single cells (or other contours) are detected by a series of steps defining respective color boundaries involving edge detection, dilation, and erosion. These feature detection steps are strengthened by segmentation and radius/area thresholding for precise detection and removal of false positives. Individually detected droplet and contour center maps are overlaid to obtain encapsulation information for further analyses. FluoroCellTrack demonstrates an average of a ~92-99% similarity with manual analysis and exhibits a significant reduction in analysis time of 30 min to analyze an entire cohort compared to 20 h required for manual quantification.

Talin-mediated force transmission and talin rod domain unfolding independently regulate adhesion signaling

Talin protein is one of the key components in integrin-mediated adhesion complexes. Talins transmit mechanical forces between β-integrin and actin, and regulate adhesion complex composition and signaling through the force-regulated unfolding of talin rod domain. Using modified talin proteins, we demonstrate that these functions contribute to different cellular processes and can be dissected. The transmission of mechanical forces regulates adhesion complex composition and phosphotyrosine signaling even in the absence of the mechanically regulated talin rod subdomains. However, the presence of the rod subdomains and their mechanical activation are required for the reinforcement of the adhesion complex, cell polarization and migration. Talin rod domain unfolding was also found to be essential for the generation of cellular signaling anisotropy, since both insufficient and excess activity of the rod domain severely inhibited cell polarization. Utilizing proteomics tools, we identified adhesome components that are recruited and activated either in a talin rod-dependent manner or independently of the rod subdomains. This study clarifies the division of roles between the force-regulated unfolding of a talin protein (talin 1) and its function as a physical linker between integrins and the cytoskeleton.

Vinculin Force-Sensitive Dynamics at Focal Adhesions Enable Effective Directed Cell Migration

Cell migration is a complex process, requiring coordination of many subcellular processes including membrane protrusion, adhesion, and contractility. For efficient cell migration, cells must concurrently control both transmission of large forces through adhesion structures and translocation of the cell body via adhesion turnover. Although mechanical regulation of protein dynamics has been proposed to play a major role in force transmission during cell migration, the key proteins and their exact roles are not completely understood. Vinculin is an adhesion protein that mediates force-sensitive processes, such as adhesion assembly under cytoskeletal load. Here, we elucidate the mechanical regulation of vinculin dynamics. Specifically, we paired measurements of vinculin loads using a Förster resonance energy transfer-based tension sensor and vinculin dynamics using fluorescence recovery after photobleaching to measure force-sensitive protein dynamics in living cells. We find that vinculin adopts a variety of mechanical states at adhesions, and the relationship between vinculin load and vinculin dynamics can be altered by the inhibition of vinculin binding to talin or actin or reduction of cytoskeletal contractility. Furthermore, the force-stabilized state of vinculin required for the stabilization of membrane protrusions is unnecessary for random migration, but is required for directional migration along a substrate-bound cue. These data show that the force-sensitive dynamics of vinculin impact force transmission and enable the mechanical integration of subcellular processes. These results suggest that the regulation of force-sensitive protein dynamics may have an underappreciated role in many cellular processes.

Breast Cancer Cells Adapt Contractile Forces to Overcome Steric Hindrance

Cell migration through the extracellular matrix is governed by the interplay between cell-generated propulsion forces, adhesion forces, and resisting forces arising from the steric hindrance of the matrix. Steric hindrance in turn depends on matrix porosity, matrix deformability, cell size, and cell deformability. In this study, we investigate how cells respond to changes in steric hindrance that arise from altered cell mechanical properties. Specifically, we measure traction forces, cell morphology, and invasiveness of MDA-MB 231 breast cancer cells in three-dimensional collagen gels. To modulate cell mechanical properties, we either decrease nuclear deformability by twofold overexpression of the nuclear protein lamin A or we introduce into the cells stiff polystyrene beads with a diameter larger than the average matrix pore size. Despite this increase of steric hindrance, we find that cell invasion is only marginally inhibited, as measured by the fraction of motile cells and the mean invasion depth. To compensate for increased steric hindrance, cells employ two alternative strategies. Cells with higher nuclear stiffness increase their force polarity, whereas cells with large beads increase their net contractility. Under both conditions, the collagen matrix surrounding the cells stiffens dramatically and carries increased strain energy, suggesting that increased force polarity and increased net contractility are functionally equivalent strategies for overcoming an increased steric hindrance.

Dietary Chrysin Suppresses Formation of Actin Cytoskeleton and Focal Adhesion in AGE-Exposed Mesangial Cells and Diabetic Kidney: Role of Autophagy

Advanced glycation end products (AGE) play a causative role in the development of aberrant phenotypes of intraglomerular mesangial cells, contributing to acute/chronic glomerulonephritis. The aim of this study was to explore mechanistic effects of the flavonoid chrysin present in bee propolis and herbs on actin dynamics, focal adhesion, and the migration of AGE-exposed mesangial cells. The in vitro study cultured human mesangial cells exposed to 33 mM glucose and 100 μg/mL AGE-bovine serum albumin (AGE-BSA) for up to 5 days in the absence and presence of 1⁻20 μM chrysin. The in vivo study employed db/db mice orally administrated for 10 weeks with 10 mg/kg chrysin. The presence of ≥10 μM chrysin attenuated mesangial F-actin induction and bundle formation enhanced by AGE. Chrysin reduced the mesangial induction of α-smooth muscle actin (α-SMA) by glucose, and diminished the tissue α-SMA level in diabetic kidneys, indicating its blockade of mesangial proliferation. The treatment of chrysin inhibited the activation of vinculin and paxillin and the induction of cortactin, ARP2/3, fascin-1, and Ena/VASP-like protein in AGE-exposed mesangial cells. Oral administration of chrysin diminished tissue levels of cortactin and fascin-1 elevated in diabetic mouse kidneys. Mesangial cell motility was enhanced by AGE, which was markedly attenuated by adding chrysin to cells. On the other hand, chrysin dampened the induction of autophagy-related genes of beclin-1, LC3 I/II, Atg3, and Atg7 in mesangial cells exposed to AGE and in diabetic kidneys. Furthermore, chrysin reduced the mTOR activation in AGE-exposed mesangial cells and diabetic kidneys. The induction of mesangial F-actin, cortactin, and fascin-1 by AGE was deterred by the inhibition of autophagy and mTOR. Thus, chrysin may encumber diabetes-associated formation of actin bundling and focal adhesion and mesangial cell motility through disturbing autophagy and mTOR pathway.

Krüppel-like factor 4 mediates cellular migration and invasion by altering RhoA activity

Kru¨ppel like factor 4 (KLF4) is a transcription factor that regulates genes related to differentiation and proliferation. KLF4 also plays a role in metastasis via epithelial to mesenchymal transition. Here, we investigate the function of Klf4 in migration and invasion using mouse embryonic fibroblasts and the RKO human colon cancer cell line. Compared to wild-type, cells lacking Klf4 exhibited increased migration-associated phenotypes. In addition, overexpression of Klf4 in Klf4^-/- MEFs attenuated the presence of stress fibers to wild-type levels. An invasion assay suggested that lack of Klf4 resulted in increased invasive capacity. Finally, analysis of RhoA showed elevated RhoA activity in both RKO and MEF cells. Taken together, our results strongly support the novel role of KLF4 in a post-translational regulatory mechanism where KLF4 indirectly modulates the actin cytoskeleton morphology via activity of RhoA in order to inhibit cellular migration and invasion.

Steps in Mechanotransduction Pathways that Control Cell Morphology

It is increasingly clear that mechanotransduction pathways play important roles in regulating fundamental cellular functions. Of the basic mechanical functions, the determination of cellular morphology is critical. Cells typically use many mechanosensitive steps and different cell states to achieve a polarized shape through repeated testing of the microenvironment. Indeed, morphology is determined by the microenvironment through periodic activation of motility, mechanotesting, and mechanoresponse functions by hormones, internal clocks, and receptor tyrosine kinases. Patterned substrates and controlled environments with defined rigidities limit the range of cell behavior and influence cell state decisions and are thus very useful for studying these steps. The recently defined rigidity sensing process provides a good example of how cells repeatedly test their microenvironment and is also linked to cancer. In general, aberrant extracellular matrix mechanosensing is associated with numerous conditions, including cardiovascular disease, aging, and fibrosis, that correlate with changes in tissue morphology and matrix composition. Hence, detailed descriptions of the steps involved in sensing and responding to the microenvironment are needed to better understand both the mechanisms of tissue homeostasis and the pathomechanisms of human disease.